Did I melt my steel pan?

Wondering if this happened to anyone else, or if anyone can explain this:

I recently picked up two Matfer Bourgeat steel pans at a garage sale. They were gently used, with just a little bit of seasoning (sort of half-gray, half-brownish, but nowhere near black). I figured I'd strip those patches of seasoning and season the pans properly, and having read about people stripping cast iron seasoning by placing pans into hot ashes from a grill/bonfire, I decided to do the same. So after using my charcoal grill for some grilling, I nestled both pans in the hot coals and (maybe foolishly) lit another chimney starter's worth of coals and dumped those on top. At this point, the pans were on top of a bed of still-hot coal (not just ash), covered with freshly lit coal.

Left the pans there overnight, and the next morning, they looked like something salvaged from the galley of the Titanic. The outside bottom of both pans was flaking off in thin, hard, brittle, razor-sharp shards: it looked like a very thin layer of steel had delaminated, and was flaking off the rest of the steel. In those places, the transition from the outside bottom to the side was now a sharp lip (instead of the usual rounded transition you have on the outside of pans). And in about a dozen places, there were what seemed like blisters or small bubbles underneath the surface.

So here's what I'm wondering, more out of curiosity than any kind of hope that I can salvage this. I was under the impression that these pans were cast from steel that was melted and poured into shape, not from sheets that were pressed together … if so, how could a thin layer at the bottom start peeling off like this? Or, could this just be how steel reacts when it's exposed to very high temperatures on the surface (thin layers separating because of high internal temp. differentials, or something)? I'm not a chemist by any means, or experienced in metallurgy; hoping somebody else is.

And just as an aside, this is by no means meant to be an indictment of these pans. I've used other ones from the same line, and they've been nothing but fantastic. Realistically, in even the most extreme cooking situations (true wok burners, and so on), they'd never encounter the kinds of temperatures they've been exposed to here. I'm posting this simply to try and understand what might have happened.